When life came along, it happened fast. Fossils suggest that microbes were present 3.7 billion years ago, just a few hundred million years after the 4.5 billion-year-old planet cooled enough to sustain biochemistry, and many researchers believe the hereditary material for these early organisms was RNA. Although not as complex as DNA, RNA would still be difficult to forge into the long strands needed to transmit genetic information, raising the question of how it could have formed spontaneously.
Now researchers may have an answer. In laboratory experiments, they showed how rocks called basalt glasses help individual letters of RNA, known as nucleoside triphosphates, bind into strands up to 200 letters long. The spectacles would be plentiful from the fire and brimstone of the early Earth; they are formed when lava is extinguished in air or water or when molten rock created by asteroid impacts cools rapidly.
The result divided the leading researchers of the origin of life. “This seems like a wonderful story that finally explains how nucleoside triphosphates react with each other to make RNA strands,” said Thomas Carell, a chemist at Ludwig Maximilian University in Munich. But Jack Shostak, an RNA expert at Harvard University, says he will not believe the result until the research team better characterizes the RNA strands.
Researchers of the origin of life love the primordial “RNA world” because the molecule can perform two different processes vital to life. Like DNA, it is made up of four chemical letters that can carry genetic information. And like proteins, RNA can also catalyze chemical reactions necessary for life.
But RNA also brings headaches. No one has found a set of plausible prebiotic conditions that would cause hundreds of letters of RNA – each of them complex molecules – to bind into strands long enough to sustain the complex chemistry needed to ignite evolution.
Stephen Moses, a geologist at the University of Colorado, Boulder, wonders if basalt glasses play a role. They are rich in metals such as magnesium and iron, which promote many chemical reactions. And, he says, “Basalt glass was everywhere on Earth at the time.”
He sent samples of five different basalt cups to the Foundation for Applied Molecular Evolution. There, Eliza Biondi, a molecular biologist, and her colleagues ground each sample to a fine powder, sterilized it, and mixed it with a solution of nucleoside triphosphates. Without the presence of glass powder, the RNA letters failed to connect. But when mixed with glass powders, the molecules combine into long strands several hundred letters long, researchers said this week in astrobiology. No heat or light was needed. “All we had to do was wait,” says Biondi. Small strands of RNA are formed after only one day, but the strands continue to grow for months. “The beauty of this model is its simplicity,” says Jan Spacek, a molecular biologist at Firebird Biomolecular Sciences. “Mix the ingredients, wait a few days and find the RNA.”
Still, the results raise many questions. One is how nucleoside triphosphates might arise in the first place. Biondi colleague Stephen Banner says recent research shows how the same basalt glasses could promote the formation and stabilization of individual RNA letters.
A bigger problem, Shostak says, is the shape of the long strands of RNA. In modern cells, enzymes ensure that most RNA grows in long linear strands. But RNA letters can also be linked in complex branching patterns. Shostak wants researchers to report the type of RNA created by basalt glasses. “I find it very disappointing that the authors made an interesting initial discovery, but then decided to stick to noise, not science,” says Shostak.
Biondi admits that her team’s experiment almost certainly produced a small amount of RNA strands. However, she notes that some branched RNA exists in organisms today and related structures may have been present at the dawn of life. She also says that other tests conducted by the group confirm the presence of long threads with connections, which most likely mean that they are linear. “It’s a healthy debate,” said Dieter Brown, a chemist about the origins of life at Ludwig Maximilian. “This will trigger the next round of experiments.”